Transients as a Probe of Massive
Black Hole Assembly
Milos Milosavljevic
California Institute of Technology
04/05/06
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Astronomical Evidence for Black Holes
R. Genzel et al. 2003,
imaged with VLT
Approximately 5-15 solar
mass black holes form in the
collapse of massive stars.
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Center of the Milky Way
contains a 4x106 solar
mass black hole.
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stellar
binarie
s
unknown
Milky Way
quasars
101
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102
103
104
105
106
107
108 109
solar masses
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Black Hole Formation
the most distant quasars
Hasinger et al. 2005
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redshift
A packet of mass m radiates energy mc2 before it enters the black hole.
The radiated power L (for “luminosity”) leaves the system.
The black hole grows by accreting packets of mass. Total cosmic mass
density in black holes is estimated by integrating the power emitted by
black holes:
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Accretion of:
•
•
•
stellar
binarie
s
ISM
Black holes
Stars
unknown
Milky Way
quasars
101
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102
103
104
105
106
107
108 109
solar masses
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Why Study Low-Mass Back Holes?
• Likely the largest number of black holes in the
universe have masses << 107 Msun.
• Low-mass black holes may be the
progenitors of “super”-massive black holes.
However we do not know how they formed,
etc.
• The low-mass black holes are sources of
gravitational radiation that will be observed by
a space-based detector.
• A wealth of data has recently become
available, but the trends are not understood. 6
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Stefan Gottloeber (AIP, Potsdam) & collaborators
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Borne et al 2000, HST/WFPC2 Mergers of
ultraluminous infrared galaxies at low
redshift.
Owen, O’Dea, Inoue, Eilek, NRAO/AUI, Twin radio
jets in Abell 400: two black holes in the same galaxy!
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NASA/CXC/MPE/S. Komossa et al.
Ultraluminous infrared galaxy NGC6240
contains two accreting black holes separated
by 2 kpc.
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Merger Finale: A Binary
Forms!
N-body simulation: Milosavljevic & Merritt 2001
10-100 pc
“Hard” binary forms when black hole
separation becomes smaller than
the radius of dynamical influence, a
< rbh
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Centers of Galaxies
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Gravitational Wave Emission
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Simulation: Frans Pretorius (U. Alberta)
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Gravitational Slingshot
Interaction
star
binary
V sin 
2U + V cos 
U
V sin 
V cos 
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The Loss Cone
circular orbit
diffusion
• Sources of diffusion of stars
in and out of the loss cone:
– “Graininess” of the stellar
gravitational potential
– Dynamical disturbances
(mergers, giant molecular
clouds, compact star clusters,
tertiary black holes, etc.)
– Brownian motion of the binary
(weak!)
• The effective volume of the
loss cone is larger for
flattened galaxies
radial orbit
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– spherical: minimal loss cone
– axisymmetric: larger loss cone
– triaxial: maximal loss cone
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galaxy merger
Milky
Way
COALESCENCE
log(decay timescale)
GALAXY MERGER
diffusio
n
binary’s semi-major axis (parsec)
The Final Parsec Problem
the bottleneck
binary forms
coalescence
black hole mass (solar mass)
log(decay radius)
(Begelman, Blandford, Rees 1980)
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cor
Gas
• Virial gas kT ~ kTvir= mpGM/r
– Primordial shock-heated gas
– Winds from evolved stars, supernovae, and AGN
– Density limited by cooling!!!
• Sub-virial gas kT < kTvir
–
–
–
–
–
Channeled to galaxy nuclei during structure formation, in mergers
Angular momentum support and circularization
Molecular maser disks: 0.1-0.5 pc, T ~ 400K, n~107-10 cm-3
AGN: r < 104 rg, T > 10,000 K, ionization, central accretion, outflows
Density limited by radiation pressure
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Mrk 896, XMM-Newton spectrum
Page et al. 2003
Narrow line Seyfert 1 galaxy,
Mblack hole ~ 106 Msun
Surface of an accretion disk
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Gas around Binary Black Holes: Alignment
(variant Bardeen-Petterson effect)
Less Precession
 prec  r7 / 2

More Precession
Gas Orbits
Gas Orbits
GG Tau: Potter/Hawaii/Gemini/AURA/NSF
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QuickT ime ™an d a
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Torque Balance and Disk Truncation
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ASC FLASH simulation,
MacFadyen & MM 2006
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QuickTime™ and a
YUV420 codec decompressor
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The Final Year
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MM & Phinney 2005
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The Final Year
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MM & Phinney 2005
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The Final Year
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MM & Phinney 2005
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Spectral Evolution
MM & Phinney 2004
after
before
Thermal accretion disk spectra
before and after decoupling and
coalescence. Thermal X-ray
emission is absent before
coalescence.
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Cosmology with Black Hole Mergers
• Gravitational wave train
– luminosity distance but not
redshift (redshift degenerate with
mass).
– localization: arcminutes to
degrees
– thousand host galaxy
candidates!
• Monitoring in X-rays at high
spatial resolution
– afterglow
– host galaxy identification,
redshift
– “standard candle” (independent
distance and redshift)
– confusion due to lensing
Holz & Hughes 2005
• Distance-redshift relation,
cosmology
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Low-Luminosity Active Galactic Nuclei
Cosmic space
density of black holes
per logarithmic X-ray
luminosity interval.
Hasinger, Miyaji & Schmidt 2005
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Contribution from Stellar Tidal Disruption to the X-ray
Luminosity Function of Active Galactic Nuclei
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NASA/CXC/SAO
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S. Komossa
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Slope sensitive to the light curve model (and maybe on the BH MF), amplitude robust
The knee reflects maximum luminosity in tidal disruption.
quasars
MM, Merritt, Ho 2006
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Conspiracy?
• Black holes with Mbh ~< 106-107
Msun:
– Preferentially occur in disk galaxies 
fueling is not merger driven.
– Could have grown to their observed
size by accreting tidally-disrupted stars
alone!
NGC6240, Max et al., Keck AO
black hole mass
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stellar velocity dispersion
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Future: MBH Assembly in the Time Domain
MacFadyen & MM, in prep.
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LSST
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Conclusions
• Black hole coalescence is expected in the merger
low-mass massive black holes (but radiation recoil
and three-body ejections may complicate retention).
• Accretion around black hole binaries and black hole
coalescence will be accompanied by a variety of
electromagnetic transients.
• Simultaneous detected of gravitational radiation and
electromagnetic emission will help measure distanceredshift relation.
• Activity from stellar tidal disruption may account for a
significant fraction of low-luminosity AGN.
• Understanding of the population of low-mass massive
black holes a top scientific priority.
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